TRANSIENT VIBRATIONS FOR TORSIONALLY FLEXIBLE ROTORS IN LARGE SYNCHRONOUS MOTOR DRIVES.

The use of high power and high speed motor drives for torsionally flexible systems can give rise to severe torque transients on start up. In this paper the transient start-up for a boiler feed pump drive is analysed. The electrical system is modelled by the conventional two-axis method. The motor power rating was of the order of 10 MW with a nominal rotational speed of 3000 RPM. The mechanical shaft was modelled by six lumped inertias connected by a series of massless torsional springs representing elements of the shaft. The inertias represent items such as impellers, couplings and a balance drum, typical of a centrifugal pump. Viscous torsional damping is added at each inertia. The overall model consists of 17 first order differential equations which are conveniently integrated using standard numerical techniques. The major items of data output are torque and speed variations for each inertia in the model. Current variation is also available.